The present invention generally relates to vehicle suspensions. More particularly, the present invention relates to elastomeric spring vehicle suspensions, such as for use in vocational or heavy haul truck applications.
Single spring rate suspensions and variable spring rate suspensions for use in vocational or heavy haul truck applications are known.
Single spring rate suspensions have a fixed spring rate that generally must be set at a level that produces a suspension with either a comfortable ride or a stiff suspension exhibiting adequate roll stability. As a result, either roll stability or ride quality is compromised in single spring rate suspensions, depending upon the selected spring rate.
Variable rate suspensions overcome this deficiency of single rate suspensions by providing for multiple spring rates during operation. As the sprung load is increased, the spring rate is correspondingly increased.
An example of a variable spring rate elastomeric spring suspension for use in vocational or heavy haul truck applications is shown in U.S. Pat. No. 6,585,286, the disclosure of which is hereby incorporated herein by reference. That suspension utilizes bolster springs and auxiliary springs to achieve its variable spring rate.
The spring rate for such a suspension can change due to the engagement or disengagement of the auxiliary spring as a function of load. The ride quality of a lightly loaded chassis having such a suspension is quite good without sacrificing roll stability at rated chassis load. When a lightly to moderately loaded chassis with such a suspension encounters moderate to large variations in roadway or operating conditions, frequent engagement and disengagement of the auxiliary spring may occur. For each such engagement or disengagement of the auxiliary spring, the spring rate for the system may undergo an abrupt change known as strike-through effect. Ride quality may be compromised as a result. Graphically, the spring rate has a discontinuity, which may be represented as a step function, at the load where the auxiliary spring is engaged or disengaged.
Prior elastomeric spring suspensions for vocational or heavy haul truck applications require their elastomeric springs to undergo loading that is compressive, tensile and/or shearing in nature. Tensile loading causes elastomeric break down.
In view of the conditions identified above with respect to prior spring vehicle suspensions for vocational or heavy haul truck applications, it is desired to provide a new and improved suspension for those applications.